Graphene oxide-carbon nanotube hybrid assemblies: Cooperatively strengthened OH···O=C hydrogen bonds and removal of chemisorbed water

Abstract

Owing to their great interest for energy storage and sensing applications, multi-layer papers consisting of graphene oxide – carbon nanotube (GO-CNT) hybrid sheets were prepared by in-situ exfoliation of graphite oxide in the presence of oxidized CNTs (oCNTs). For the first time we elucidate the influence of oCNTs on chemisorbed water (CW), i.e. water molecules inherently bound to oxygen functional groups (OFGs) of graphene oxide (GO) and responsible for irreversible structural damage upon thermal reduction processes. We show that oCNTs self-assemble onto GO sheets during the liquid phase processing steps by forming cooperatively strengthened OH···O=C hydrogen bonds between the carboxylic groups of oCNTs and OFGs of GO. At oCNT contents of about 10 to 15 wt. % this leads to the displacement of considerable amounts of CW without altering the original chemical composition of GO. Thermally reduced GO-CNT (rGO-CNT) papers reveal improved sp2 character and an enhancement of the specific capacitance by 75% with respect to thermally reduced GO (rGO), largely due to the effective removal of CW by oxidized CNTs. These findings disclose the relevance of cooperative hydrogen bonding phenomena in graphene oxide paper/film electrodes for the development of improved electrochemical energy storage and sensing devices.